The invention relates to a cover band assembly of a blade row of stator or rotor blades.
The aerodynamic resilience and efficiency of turbines is limited by the growth and detachment of boundary layers on the blades as well as on the hub and housing walls. In the state of the art, solutions for this fundamental problem could be provided only to a limited extent. One source for the losses which occur in turbines is the leakage flow about the blade cover bands, such as can often be found at the inner blade end of stators or at the outer blade end of rotors. Usually the leakage flow is kept small through sealing tips or other sealing means that are arranged inside the cavity in which the cover band is embedded. Still the leakage flow can have extremely detrimental effects on the performance of the turbine, in particular in highly loaded blade rows that are characterized by a high static pressure drop and thus a strong propulsion of the leakage flow.
In cover band assemblies according to the state of the art, the leakage flow is substantially determined by the gap that is left by the sealing means between stationary and rotating components. The sealing gap is usually formed between sealing tips and a contour that is arranged opposite the sealing tips. Here, the leakage flow strongly increases with the aerodynamic load and the sealing gap width that is chosen for the blade row to which the cover band is applied. This results in poor characteristic operating values with respect to the level of efficiency and the width of the turbine's operating range.